The field of solenoids includes the following United States patents.
Ojima, et al. in U.S. Pat. No. 4,419,643 shows a Self-Sustaining Solenoid which includes a moving iron core which is attracted into a coil to be received by a fixed receiver. A magnetic yoke extends between the fixed receiver and the surface of the moving iron cove.
Luckenback in U.S. Pat. No. 4,327,344 shows a Solenoid with Mechanically Latchable Plunger which includes a single coil and a single armature plunger which has a latch pin. A pulse of current applied to the coil moves the armature plunger to a first retracted position and a spring biased latch latches the armature plunger. A subsequent energization of the coil unlatches the armature plunger so that the armature plunger is returned to the original position by a spring.
Fuzzell in U.S. Pat. No. 4,494,096 shows a Latching Solenoid which includes a first coil which positions a member at a preselected location where it is locked by a mechanical latch. The latch includes a movable plunger which engages an end portion of the member. Inserting the plunger into the member radically expands the end portion and captures the end portion between the plunger and the wall of a bore. A second coil withdraws the plunger and releases the member from the latched position.
Kelly in U.S. Pat. No. 4,613,176 shows a Door Latch Mechanism which has a pivoted latch which is disposed between a retaining solenoid and a four-bar toggle linkage. The toggle linkage connects an operating stem of the retaining solenoid to a latch. The linkage provides a mechanical advantage to amplify the holding force of the solenoid. When the solenoid is de-energized and pressure is applied to open the door, the latch pivots and the linkage collapses to release a keeper bar.
Green, Jr. in U.S. Pat. No. 4,752,487 shows a Double Acting Permanent Magnet Latching Solenoid which is driven by reversal of coil current and held in place by a permanent magnet. The permanent magnet is located in a space between two coils. The device includes conical ends on the solenoid plunger and conical interiors matching the conical ends.
Laffey in U.S. Pat. No. 5,808,534 shows a Solenoid Frame and Method of Manufacture which includes a frame with interlocking tabs and a locking mechanism for fastening the frame and pieces.
Hines in U.S. Pat. No. 5,365,210 shows a Latching Solenoid with Manual Override which includes a manually translatable member which can be moved to vary the reluctance in a magnetic circuit.
Cascolan, et al. in U.S. Pat. No. 6,265,956 shows a Permanent Magnet Latching Solenoid which includes a bushing which is press-fit in each of the ends of a bobbin. A magnetically permeable frame surrounds the bobbin and openings in the ends of a frame accommodate passage of an operator rod which is attached to an armature. Brief pulsing of a coil on the bobbin creates an opposing magnetic field which temporarily opposes the magnetic field on the first end of the frame and creates an attractive field at the opposite end of the frame thereby impelling the armature from a first end position to a second end position.
Ruan, et al. in U.S. Patent Application Publication US 2003/0137374 A1 shows Micro-Magnetic Latching Switches with a three-dimensional solenoid coil which includes a moveable cantilever which has a magnetic material. The cantilever includes a conducting layer. A permanent magnet induces magnetization in the magnetic material and a solenoid produces a second magnetic field to switch the cantilever between a first stable state and a second stable state.
Despite the developments of the prior art there remains a need for a relatively small light-weight linear latching solenoid.